Axial T2-weighted MR image shows an exostosis with a bright cartilagenous cap (arrowheads), which is thin and smooth.
This is a classic radiographic appearance of ‘sessile osteochondroma’ at the most common location (metaphysis) of bone.
Facts:
Most common benign bone tumor
Due to aberrant epiphyseal development
Growth stops after skeletal maturation
Malignant transformation in 1-2% of solitary lesion
Points:
Suspect malignant transformation if: growth after skeletal maturation, pain in the absence of fracture, bursitis or nerve compression
MRI and CT to demonstrate thickness of cartilaginous cap, if >2 cm suspect malignancy
Reference:
Stoller et al. Diagnostic Imaging: Orthopedics. 2004
Image Courtesy of RadiologyinThai.com
